Transcriptional analysis of different mulberry cultivars in response to ralstonia solanacearum

Bacterial wilt caused by Ralstonia solanacearum is a major disease of the mulberry (Morus atropurpurea Roxb.), resulting in severe yield and quality losses. However, little is known about the molecular mechanisms of resistance. Using the RNA sequencing technique, we identified early transcriptional changes in resistant (KQ10 and YS283) and susceptible (YSD10) mulberry cultivars in response to R. solanacearum infection. We observed that 798 genes were differentially and specifically regulated in both resistant cultivars but not in the susceptible cultivar after infection with R. solanacearum, including 502 upregulated and 296 downregulated genes. Among the differentially expressed genes, 31 encode transcription factors and 48 encode protein kinases. Interestingly, we found that a large number of genes (61) associated with cell-wall modification were differentially and specifically regulated in the resistant cultivars. These genes could be divided into 10 major groups. The largest group is the glucosyltransferase family, followed by the pectinesterase inhibitor, glucanase, and glycoprotein families, suggesting that cell-wall modifications may play an important role in resistance levels in mulberry. This transcriptional analysis paves the way for elucidating the molecular mechanisms of the resistance response to R. solanacearum in mulberry. Key words: mulberry, transcriptional analysis, disease resistance, Ralstonia solanacearum, cell wall. La fletrissure bacterienne causee par Ralstonia solanacearum est une maladie importante du murier (Morus atropurpurea Roxb.) qui entraine des pertes severes de rendement et de qualite. Cependant, les mecanismes moleculaires de resistance sont peu connus. A l'aide d'une technique de sequencage de l'ARN, nous avons identifie des changements transcriptionnels precoces chez des cultivars resistants (KQ10 et YS283) et sensibles (YSD10) du murier en reaction a l'infection de R. solanacearum. Nous avons observe que 798 genes etaient regules de facon specifique et differentielle chez les deux cultivars resistants mais ne l'etaient pas chez le cultivar sensible apres une infection de R. solanacearum, incluant 502 genes regules a la hausse et 296 genes regules a la baisse. Parmi les genes exprimes de facon differentielle, 31 encodaient des facteurs de transcription et 48 encodaient des proteines kinases. Fait interessant, nous avons trouve qu'un grand nombre de genes (61) associes a la modification de la paroi cellulaire etaient regules de facon specifique et differentielle chez les cultivars resistants. Ces genes pouvaient etre divises en deux grands groupes. Le plus gros groupe est compose de la famille des glucosyltransferases suivi des familles de l'inhibiteur de la pectase, de la glucanase et des glycoproteines, ce qui signifie que les modifications de la paroi cellulaire pourraient jouer un role important dans le degre de resistance du murier. L'analyse transcriptionnelle prepare la voie pour elucider les mecanismes moleculaires de la reaction de resistance a R. solanacearum chez le murier. [Traduit par la Redaction] Mots-cles : murier, analyse transcriptionnelle, resistance aux maladies, Ralstonia solanacearum, paroi cellulaire.
Introduction Mulberry (Morus atropurpurea Roxb.) is an important commercial woody plant, which is widely cultivated in many tropical and subtropical areas--especially in developing countries in Asia and Africa--because its leaves [...]